Authorities’ quick response to find the shooter responsible for killing at least 50 people at the Route 91 Harvest Festival at the Las Vegas Strip has some wondering how they could find him so fast in a hotel that has 45 floors.

Turns out it wasn’t the muzzle flashes or noises from the rifle but the smoke alarm that led the SWAT team to find 64-year-old Stephen Paddock.

Without that indicator, the team would have had to search 3,309 rooms and a 135,000-square-foot casino, reported the Washington Post.

When the SWAT team arrived at the correct room, they used explosives to open the door, but Paddock was already dead. Las Vegas Sheriff Joe Lombardo confirmed that Paddock committed suicide before authorities could reach him.

"He rained down hell on those people," Sutton told The Washington Post. "Hundreds of rounds. The sheriff said that there were several firearms found in the room. He was extremely well armed. He must have brought plenty more ammunition, already loaded into magazines."

Police believe that Paddock had been staying at the hotel since Thursday.